If they have flat batteries you could be safe if they are LiFePO which are quite hard to light on fire. YMMV depending on the actual battery. Usually the come from batches of old phones which went out of production are put into these kind of things since they can be bought on the cheap.
If they put in a round cell I'd stay away. I usually replace the cell with one I know is good and check the circuit for protection. Wouldn't be the first time I've seen something with no over or undervolt protection whatsoever.
No phones use this chemistry. I have no idea what you're on about.
>Wouldn't be the first time I've seen something with no over or undervolt protection whatsoever.
Even the cheapest lithium ion charge controllers have overvolt protection by the nature of how they work. What can happen however is a controller could be specced to charge to 4.3V per cell and a 4.2V cell is instead installed. This is a problem.
If they put in a round cell I'd stay away. I usually replace the cell with one I know is good and check the circuit for protection. Wouldn't be the first time I've seen something with no over or undervolt protection whatsoever.